Among biodegradable resins, a polylactic acid resin is inexpensive because L-lactic acid used as a raw material is produced by a fermentation method using a sugar extracted from maize, potatoes, or the like. Also, the polylactic acid resin has a very low amount of a total carbon oxide discharge because the raw material is plant-derived, and the properties of the resin include strong rigidity and high transparency. For these and other reasons, the utilization of polylactic acid resins is expected to be promising at present.
However, in addition to the properties mentioned above, since polylactic acid resin also has the properties of being brittle and hard, and lacking flexibility, its applications are limited, so that there are hardly any practical achievements in the fields of daily sundries, household electric appliance parts, automobile parts, or the like. In addition, when the resin is molded into an injection molded article or the like, there are some disadvantages such as mechanical strength such as flexibility or impact resistance is insufficient, and whitening upon bending or worsening of hinge properties takes place, so that the resin is not used at present.
On the other hand, the polylactic acid resin has a delayed crystallization velocity, and has an amorphous state after being injection-molded, so long as a mechanical processing such as stretching is not carried out. The polylactic acid resin has a low glass transition temperature (Tg) of 60° C., so that there is a disadvantage that the resin cannot be generally used under an environment condition of a temperature of 55° C. or higher, thereby being disadvantageous in heat resistance.
Further, in order to utilize the polylactic acid resin in durable materials such as household electric appliance parts or automobile parts, aside from being provided with heat resistance and mechanical strength, the polylactic acid resin having a certain level of flexibility is in demand.
On the other hand, a technique of adding an inorganic filler as a reinforcing material is known. In a case where a resin is biodegradable, the inorganic filler is also required to be biodegradable, and a cellulose is used as the inorganic filler (see, for example, JP-A-2006-63111 and JP-A-2003-128791).
In addition, it is reported that use of a cellulose having a high crystallinity is effective, from the viewpoint of improving the strength of a resin molded article (see JP-A-2006-316253).